Electrodeposition of platinum metals



Patented Oct. 28, 1930 UNITED STATES PATENT OFFICE HERBERT mun ZSCHIEGNEB, OI WOODBRIDGE, NEW JERSEY, ASSIGNOB, BY will! ASSIGNMENTS, TO BAKER & 00., INC., 0]? NEWARK, NEW JERSEY, A. CORPORATION 0! NEW JERSEY ELEC'IBODEPOSITION OF PLATINUM. mus

Io Drawing.

This invention relates to the electro-deposition of platinum metals and especially to the electro-deposition of metals of the group compalladous chloride (PdCl 2H O) or rhodium trichloride RhCl are preferable; to this solution I add an excess of sodium nitrite and heat until the color change indicates a reaction after which I make the hot solution ammoniacal with ammonium hydroxide. In the first part of this reaction, the sodium nitrite reacts with the metal chloride and forms a double nitrite of sodium and the metal, and upon the subsequent addition of ammonium hydroxide, as stated, an ammino nitrite of the metal is formed in solution in the ammoniacal bath and from such a bath the metal can be electrodeposited.

The electro-deposition is done from the hot solution with a potential of 4 to 10 volts and a current of 0.05 to 0.20 amperes per square inch. An insoluble anode such as platinum or other precious metal, graphite, etc. may be used.

I have also found that alloys of the metals platinum, palladium and rhodium can be electrodeposited from my bath if it be prepared from ammino nitrites of the metals to be deposited. The preparation and use of such an alloy plating bath is analogous to the preparation and use of a single metal bath, as is more fully set forth hereinafter.

Further details of my bath'and procedure are given in the following examples which show the preparation and use of a platinum plating bath and a platinum-rhodium alloy bath.

Example I.2 grams of chloroplatinic acid were dissolved in 140 c. c. distilled water and 3 grams of sodium nitrite added. This 4 Application flied October 7, 1927. Serial Io. 224,704.

solution was now heated at 85 to 90 C. until the orange color of the original solution was changed to colorless or a very pale yellow. This color change probably indicates a reduction from tetravalent to divalent platinum to form the complex salt sodium platinum nitrite. 5 c. c. of ammonium hydroxide (sp. gr. 0.90) was now added forming a platinum ammino nitrite after which the solution was ready for use.

The object to be plated was made the cathode and an anode of platinum was provided. I have found that the best results were obtained at 7 volts with a current density of 0.05 to 0.08 amperes per square inch of cathode surface while the bath is maintained at 7 5-95 C. A bright adherent plate of platinum was obtained.

Emample Il.+1.8 ams platinum chloride and 0.2 grams rho ium chloride were dissolved in 140 c. c. distilled water and 3 grams sodium nitrite added. This solution was now heated at 8590 C. until a change of color to a very pale yellow took place. 5 c. c. of ammonium hydroxide solution was now added. This solution when used as the electrolyte as described above with a platinum anode gave an adherent cathode deposit of approximately 90% platinum and 10% rhodium.

The ammino nitrite solutions are especially adapted for plating the precious metals on copper, nickel, gold or alloys such as brass or white gold, and other precious metal alloys used in ewelry or scientific instruments.

I have found that the concentration of my plating bath can be considerably varied and still good plating results will be obtained, and I do not wish to be limited to the exact quantities given. I have increased the platinic chloride concentration up to 3 times that given; the amount of nitrite and ammonia added is not critical and the proportions have been doubled and tripled without harmful efi'ects. Potassium or ammonium nitrite may be used.

Claims:

1. An electrolyte for the electro-deposition of a metal of the group comprising platinum, palladium and rhodium, comprising the heat treated aqueous solution of a chloride of said metal and an excess of sodium nitrite containing an excess of ammonia.

2. An electrolyte for the electrode -osition of a metal of the group, platinum, pa ladium and rhodium, comprising an ammoniacal aqueous solution of the reaction product of a chloride of the metal with an alkali metal nitrite.

3. An electrolyte for the electrode osition of a metal of the group, platinum, pa ladium and rhodium, com rising an ammoniacal aqueous solution 0 the reaction product of the chloride of the metal with sodium nitrite'.

4. An electrolyte for the electrodeposition of platinum comprising an ammoniacal aqueous solution of the reaction product of a chloride of platinum with an alkali metal nitrite.

5. An electrolyte for the electrodeposition of platinum comprising an ammoniacal aqueous solution of the reaction product of a chloride of platinum with sodium nitrite.

6. Method of preparing an electrolyte for the electrodeposition of metals of the group comprising platinum, palladium and rhodium which comprises treating an aqueous solution of a chloride of the metal to be deposited with an excess of an alkali metal nitrite until a reaction has taken place and then adding an excess of ammonia.

'7. Method for the preparation of an electrolyte for the electro-deposition of a. metal or alloy of the group comprising platinum, palladium and rhodium which comprises treating an aqueous solution of a chloride of said metal with an excess of sodium nitrite until a reaction has taken place and then adding an excess of ammonia.

8. An electrolyte for the electrodeposition of a metal or alloy of the group platinum, palladium and rhodium, containing in solution an ammino nitrite of the metal to be deposited, the electrolyte being ammoniacal.

9. An electrolyte for the electrodeposition of platinum containing in solution an ammino nitrite of platinum, the electrolyte being ammoniacal.

Signed at Perth Amboy in the county of Middlesex and State of New Jersey this 3rd day of October, A. D. 1927.

HERBERT EMIL ZSGHIIEIGNER. 

